Two classes of glomerular basal laminas are identified with a newly developed guanidine technique. The electron-opaque epithelial basal lamina is the most prominent element of the glomerular basal lamina scaffold. It is a continuous layer within each glomerulus, folding into capillary tufts and loops, but never completely encircling the entire circumference of each capillary, similar to the serosa covering the intestinal loop and mesentery. The vascular space so defined is further partitioned into individual capillary lumen by an electron-lucent mesangial basal lamina, that forms a meshwork continuous with the vascular pole of the glomerulus and extends peripherally to surround capillary lumens. The latter, designated endothelial basal lamina, is extremely attenuated and appears as a vestigial structure in glomerular capillary loops. Changes in juxtamesangial epithelial basal lamina indicate that it may be the site of the bulk removal and renewal of the epithelial basal lamina.
The unique epithelial origin of glomerular capillary basal lamina and its organization provide a structural basis for understanding the glomerular physiology gained by various tracer studies. The results also suggest that the guanidine technique may be a useful new approach to the analysis of basal lamina alterations in various glomerular diseases.